Jian-Hua Qian

Why Precipitation Is Mostly Concentrated over Islands in the Maritime Continent

Abstract High-resolution observations and regional climate model simulations reveal that precipitation over the Maritime Continent is mostly concentrated over islands. Analysis of the diurnal cycles of precipitation and winds indicates that this is predominantly caused by sea-breeze convergence over islands, reinforced by mountain–valley winds and further amplified by the cumulus merger processes. Comparison of a regional climate model control simulation to a flat-island run and an all-ocean run demonstrates that the underrepresentation of islands and terrain in the Maritime Continent weakens the atmospheric disturbance associated with the diurnal cycle, and hence underestimates precipitation. The implication of these regional modeling results is that systematic errors in coarse-resolution global circulation models probably result from insufficient representation of land–sea breezes associated with the complex topography in the Maritime Continent. It is found that precipitation in the Maritime Continent, ...

Reinitialized versus Continuous Simulations for Regional Climate Downscaling

The methodology for dynamical climate downscaling is studied using the second-generation regional climate model (RegCM2). The question addressed is, in order to simulate high-resolution details as accurately as possible, what strategy should be taken: continuous long-term integration in climate prediction mode or consecutive shortterm integrations in weather forcasting mode? To investigate this problem, the model was run for 5 months in three different ways: 1) a 5-month continuous simulation, 2) monthly reinitialized simulations, and 3) 10-day reinitialized simulations. Compared to the observed precipitation, the 10-day reinitialized simulation results in the smallest error, while the continuous run shows larger error. Analysis shows that the long-term continuous simulation is contaminated by the systematic errors associated with the steep Andes Mountains and the uncertainties in the moisture processes in the planetary boundary layer near the coast. The method of 10-day reinitialization effectively mitigates the problem of systematic errors and makes a difference in the subtle precipitation processes in the regional climate model, therefore improving the accuracy in dynamic downscaling.

Interactions among ENSO, the Monsoon, and Diurnal Cycle in Rainfall Variability over Java, Indonesia

Abstract Using a high-resolution regional climate model—the Abdus Salam International Centre for Theoretical Physics Regional Climate Model version 3 (RegCM3)—and station and satellite observations, the authors have studied the spatial heterogeneity of climate variability over Java Island, Indonesia. Besides the well-known anomalous dry conditions that characterize the dry and transition seasons during an El Nino year, analysis of regional model output reveals a wet mountainous south versus dry northern plains in precipitation anomalies associated with El Nino over Java during the peak rainy season. Modeling experiments indicate that this mountains/plains contrast is caused by the interaction of the El Nino–induced monsoonal wind anomalies and the island/mountain-induced local diurnal cycle of winds and precipitation. During the wet season of El Nino years, anomalous southeasterly winds over the Indonesian region oppose the climatological northwesterly monsoon, thus reducing the strength of the monsoon wi...

A Global Nonhydrostatic Semi-Lagrangian Atmospheric Model without Orography

Abstract A global nonhydrostatic semi-implicit semi-Lagrangian (SISL) atmospheric model with orography has been developed. The height-based terrain-following σz coordinate of Gal-Chen and Somerville is used to incorporate the orography. A 3D vector form of the SISL formulation is proposed. It is based on the complete Navier–Stokes equations. The model is stable for large time steps of up to 1 h at horizontal/vertical resolution of 2.8125°/1200 m. Isolated bell-shaped mountain profiles and real orography are employed to evaluate the model performance. The sensitivity of the model with orography to the order of accuracy of the uncentering scheme, the reference temperature (T), and size of the time step are similar to that of the model without orography described in Semazzi et al. The authors find that for successful execution of the model, it is important that the orographic height Zs, the reference state mass variable (qs), and T satisfy the hydrostatic balance relationship in the terrain-following σz coor...

Mechanisms for Torrential Rain Associated with the Mei-Yu Development during SCSMEX 1998

A case of torrential precipitation associated with the mei-yu front, an Asian summer monsoon system east of the Tibetan Plateau, is studied using the coupled fifth-generation Pennsylvania State University‐NCAR Mesoscale Model (MM5) and the NASA Goddard Space Flight Center Parameterization for Land‐Atmosphere‐Cloud Exchange model. The impact of both remote and local sources of water vapor on the location and intensity of mei-yu precipitation are studied by numerical experiments. The results demonstrate that the main source of water vapor for this heavy precipitation event over the Yangtze River Valley is the Bay of Bengal. Moisture is transported by a southwesterly low-level jet (LLJ) southeast of the Tibetan Plateau. Although the LLJ is largely manipulated by large-scale forcing, the mesoscale circulation that results from mei-yu condensational heating acts to increase the maximum wind speed of the jet. The condensation-induced local circulation strengthens the moisture transport in the LLJ, providing a positive feedback that sustains the mei-yu precipitation system. Precipitation recycling increases the total precipitation in the Yangtze River Valley only slightly, but it tends to shift the maximum rainfall center toward the warmer side of the mei-yu rain belt. This shift is due to the pronounced increase in atmospheric moisture and decrease in surface temperature over the warm side of the rain belt.

Regional Climate Model–Simulated Timing and Character of Seasonal Rains in South America

Abstract The potential of an experimental nested prediction system to improve the simulation of subseasonal rainfall statistics including daily precipitation intensity, rainy season onset and withdrawal, and the frequency and duration of dry spells is evaluated by examining a four-member ensemble of regional climate model simulations performed for the period 1982–2002 over South America. The study employs the International Centre for Theoretical Physics (ICTP) regional climate model, version 3 (RegCM3), driven with the NCEP–NCAR reanalysis and the European Centre–Hamburg GCM, version 4.5. Statistics were examined for five regions: the northern Amazon, southern Amazon, the monsoon region, Northeast Brazil, and southeastern South America. RegCM3 and the GCM are able to replicate the distribution of daily rainfall intensity in most regions. The analysis of the rainy season timing shows the observed onset occurring first over the monsoon region and then spreading northward into the southern Amazon, in contras...

Diurnal Cycle in Different Weather Regimes and Rainfall Variability over Borneo Associated with ENSO

AbstractThe interannual variability of precipitation over the island of Borneo in association with El Nino–Southern Oscillation (ENSO) has been studied by using the Global Precipitation Climatology Centre (GPCC) gridded rain gauge precipitation, the NOAA Climate Prediction Center (CPC) Morphing Technique (CMORPH) satellite estimated precipitation, the Quick Scatterometer (QuikSCAT) satellite estimated sea winds, and the National Centers for Environmental Prediction (NCEP)–National Center for Atmospheric Research (NCAR) reanalysis data. Analysis of the GPCC precipitation shows a dipolar structure of wet southwest versus dry central and northeast in precipitation anomalies associated with El Nino over Borneo Island during the austral summer [December–February (DJF)]. By using the 0.25° and 3-hourly CMORPH precipitation, it is found that rainfall over Borneo is strongly affected by the diurnal cycle of land–sea breezes. The spatial distribution of rainfall over Borneo depends on the direction of monsoonal wi...

Analysis of field oriented control for permanent magnet hysteresis synchronous motors

A microprocessor implementation of the field-oriented control scheme for the permanent magnet (PM) hysteresis synchronous motor is reported. The basic principle is to decouple the torque-current component from the flux-current component so that these two components can be independently controlled. A d-q axis model of the PM hysteresis synchronous motor is presented, and the field-oriented control obtained from the basic machine model. A control scheme that decouples the stator current components and orients it to the rotor frame is described. A scheme for detecting the rotor position is proposed. A software package based on the Intel 8086 microprocessor has been developed. A sine PWM voltage source inverter is used in the experimental work. The test results validate the theoretical steady state and dynamic performances of the laboratory prototype motor. >

Prediction of Rice Production in the Philippines Using Seasonal Climate Forecasts

Predictive skills of retrospective seasonal climate forecasts (hindcasts) tailored to Philippine rice production data at national, regional, and provincial levels are investigated using precipitation hindcasts from one uncoupled general circulation model (GCM) and two coupled GCMs, as well as using antecedent observations of tropical Pacificseasurfacetemperatures,warmwatervolumes(WWV),and zonalwinds(ZW).Contrastingcross-validated predictive skills are found between the ‘‘dry’’ January‐June and ‘‘rainy’’ July‐December crop-production seasons. For the dry season, both irrigated and rain-fed rice production are shown to depend strongly on rainfall in the previous October‐December. Furthermore, rice-crop hindcasts based on the two coupled GCMs, or on the observed WWV and ZW, are each able to account for more than half of the total variance of the dry-season national detrended rice production with about a 6-month lead time prior to the beginning of the harvest season. At regional and provincial levels, predictive skills are generally low. The relationships are found to be more complex for rainyseason rice production. Area harvested correlates positively with rainfall during the preceding dry season, whereas the yield has positive and negative correlations with rainfall in June‐September and in October‐December of the harvested year, respectively. Tropical cyclone activity isalso shown to be a contributing factor in the latter 3-month season. Hindcasts based on the WWV and ZW are able to account for almost half of the variance of the detrended rice production data in Luzon with a few months’ lead time prior to the beginning of the rainy season.

A role for tropical tropospheric temperature adjustment to El Niño–Southern Oscillation in the seasonality of monsoonal Indonesia precipitation predictability

(1) We describe the seasonality in the variability and predictability of Indonesian monsoonal climate, dominated by the El Nino-Southern Oscillation (ENSO) phenomenon, and interpret it in light of theories of the development of the global ENSO teleconnection which explain the evolution of the response of the tropical ocean- atmosphere to ENSOs perturbation. High predictability during the dry and transition seasons, which coincide with ENSO growth, is expected from the coherent large-scale response to ENSOs initial perturbation. As the tropical ocean-atmosphere equilibrates to ENSO, and ENSO itself begins to decay, its direct influence diminishes, and regional features associated with the delayed response to ENSO become more prominent. Consistent with this interpretation, in a preliminary observational analysis of station data over Jawa we find that predictability is high during the growth phase of ENSO. We also find that at these regional scales there may be more predictability than previously thought as ENSO decays. Finally, we show that a simple one-tier prediction system, i.e., a system where the evolution of oceanic and atmospheric anomalies is internally consistent, better captures the intrinsic coupled nature of the ENSO teleconnection, compared to a two-tier system where the ocean forces the atmosphere, but does not respond to its feedback.